The current trend towards miniaturization, e.g. of MEMS microphones (MEMS=micro-electromechanical system), demands for smaller electric or mechanic or electromechanical devices. In general, MEMS microphones comprise a flexible or movable membrane and a rigid back plate. The membrane and the back plate act as electrodes of a capacitor. The influence of received sound and its respective air pressure changes result in a changing capacity of such a MEMS capacitor. In MEMS microphones, this changing capacity is converted into an electrical signal by means of an applied DC bias voltage in the range of 10 V.
The area of respective capacitor electrodes provides a capacity in the range of 1 pF. As an effect of the miniaturization, the respective electric signal levels are relatively weak. For that, a signal amplifier such as a low noise amplifier with a very high input impedance is needed. The impedance of the input side of the signal amplifier is typically in the range of 1 TΩ.
From U.S. Published Application No. 2009/0001553 A1, MEMS microphones are known.
What is needed is a low noise MEMS microphone that is producible in a cost-efficient manner especially on low-cost substrates.